Heat-seal device

ABSTRACT

A heat-seal device generally includes a heat source, a thermal conductor, which encapsulates at least a portion of the heat source and is capable of transferring heat from the heat source, and a thermal insulator, which substantially surrounds the thermal conductor but leaves a portion thereof exposed, the exposed portion of the thermal conductor providing a heat-seal contact surface, which is adapted to be brought into contact with a material to be sealed.

BACKGROUND OF THE INVENTION

The present invention relates to a device for sealing materials such asplastic film and, more particularly, to an improved heat-sealing devicehaving a heat-source encapsulated within a thermal conductor.

Various types of machines exist for forming containers from plasticfilms. In such machines, one or more heat-sealing devices are includedfor sealing together the plastic films in such a manner as to createand/or seal-closed the containers.

In the field of packaging, for example, many types of machines forminflated packaging cushions by inflating a flexible container, e.g. abag, with air, and then sealing closed the inflated container. Theinflatable containers may be pre-formed and arranged in series in aflexible web, with only a longitudinal closure seal being formed at theopening of the containers by the heat-sealing device, wherein“longitudinal” refers to the direction in which the web moves as it isconveyed through the machine. Alternatively, the containers may beformed from a pair of juxtaposed film plies, wherein one heat-sealdevice forms a longitudinal seal between juxtaposed edge regions of thefilms to form a closed longitudinal edge, while leaving the opposinglongitudinal edge open; another heat-seal device creates transverseseals between the two film plies to form the containers, with the openlongitudinal edge providing openings in the containers for inflation;and a third heat-seal device forms a longitudinal seal at the openlongitudinal edge to seal-closed the openings after the containers havebeen inflated. Alternatively, a single film ply may be used, which is‘center-folded’ in the longitudinal direction such that the fold formsthe closed longitudinal edge; in this case, only one longitudinalheat-seal device is required. Examples of such machines may be found,for example, in U.S. Pat. Nos. 6,598,373, 7,220,476, and 7,225,599.

Another method for producing packaging cushions is known as‘foam-in-place’ packaging, wherein a machine produces flexiblecontainers, e.g., bags, from flexible, plastic film, and dispenses a,foamable composition into the containers as they are being formed. Asthe composition expands into a foam within the container, the containeris sealed shut and typically dropped into a carton, e.g., a box, whichholds the object to be cushioned. The rising foam expands into theavailable space within the carton, but does so inside the container.Because the bags are formed of flexible plastic, they form individualcustom foam cushions around the packaged objects. As part of thecontainer-forming mechanism, a heat-seal device is generally providedfor forming a longitudinal heat-seal. Exemplary types of such packagingapparatus are described, for example, in U.S. Pat. Nos. 4,800,708,4,854,109, 5,027,583, 5,376,219, 6,003,288, 6,472,638, 6,675,557, and7,607,911, and in U.S. Pub. No. 2007-0252297-A1.

While the foregoing machines for making air-filled and foam-filledpackaging cushions have been widely used and commercially successful,improvement is continually sought. One particular aspect whereinimprovement is desired concerns the manner in which the film plies aresealed together, especially in the longitudinal direction, i.e., thedirection in which the film plies move as they are conveyed through themachine.

The inventors hereof have determined that an important factor in makinggood heat seals is consistency in the temperature at which heat isapplied to the films during the formation of the seal. The selection ofthe correct temperature to be applied during heat-sealing is commonlycarried out by operators of cushion-making machines through routineexperimentation, e.g., by trial and error. If the temperature is toohigh, the heat-seal device may melt through the films without sealingthem together; if the temperature is too low, no seal or anincomplete/weak seal may be formed. The correct temperature to beselected will vary from application to application, based on a number ofoperational factors, including the composition and thickness of the filmplies to be sealed, the pressure at which the film plies and the heatingdevice are urged together, the speed at which the film is conveyed, etc.Mathematical algorithms may also be used to select to optimumtemperature, e.g., based on operator input and/or sensor input of theforegoing factors.

In addition to the selection of the proper heat-sealing temperature, afactor that is equally important to the formation of good, consistentheat seals is the ability of the heat-seal device to maintain theselected temperature during the formation of the heat seals. A number offactors can influence the temperature of the heat-seal device, includingthe speed at which the film is conveyed through the machine. In manypackaging-cushion machines, the film is driven at varying speeds throughthe machine. As the film is driven faster, it has more ability to removeheat from the heat-seal device, necessitating higher wattage (electricalpower) to maintain the proper temperature. Conversely, as the filmdrives more slowly, it does not use the heat as fast, requiring lesspower to make the seal. Other factors involved in determining the powernecessary to make a sufficient seal include ambient temperature, latentheat build-up in the sealing components, the thickness of the filmmaterial, and the temperature of the film itself, e.g., a new roll offilm may be taken from a cool storage room and installed on the machine,where it will slowly raise to ambient temperature.

While conventional packaging-cushion machines typically have means forcontrolling the temperature of the heat-seal device to achieveconsistency, improvement is sought in order to obtain a higher degree ofprecision, i.e., a lower degree of temperature variation from a selectedtemperature.

Another aspect of conventional heat-seal devices for which improvementis sought concerns the structure of such devices. Conventional heat-sealdevices employ, as a heat-source, an electrically-resistive heatingelement, which generates heat upon the passage of electricitytherethrough. Such heating elements are typically fully exposed, andbrought into direct contact with the film to be sealed, which can resultin melt-throughs of the film plies. When the heat-seal device meltsthrough the film plies, an outer strip from one or both film plies veryoften separates from the rest of the film and wraps around the heat-sealdevice. This problem, which is known as ‘ribbon cutting,’ results in thenecessity of shutting down the cushion-making machine and extricatingthe film strip from the heat-seal device. Typically, the strip istightly wound around the device and/or partially melted such thatremoval of the strip is a difficult and time-consuming process. Anotherdisadvantage of ‘open-air’ heating elements is that such configurationlimits the service life of the heating element due to frictional contactwith the film and oxidation due to exposure to the air while heated.

Therefore, the need exists for an improved heat-seal device that issuitable for forming heat-seals in packaging-cushion machines, and whichavoids the foregoing disadvantages.

SUMMARY OF THE INVENTION

That need is met by the present invention, which, in one aspect,provides a heat-seal device, comprising:

a. a heat source;

b. a thermal conductor, which encapsulates at least a portion of theheat source and is capable of transferring heat from the heat source;and

c. a thermal insulator, which substantially surrounds the thermalconductor but leaves a portion thereof exposed, the exposed portion ofthe thermal conductor providing a heat-seal contact surface, which isadapted to be brought into contact with a material to be sealed, whereinthe thermal conductor has a higher degree of thermal conductivity thanthe thermal insulator.

Another aspect of the invention pertains to a heat-sealing method,comprising the steps of:

a. providing the heat-seal device described above;

b. causing the heat source to produce heat; and

c. bringing the heat-seal contact surface into contact with a materialto be sealed,

whereby, the heat produced by the heat source transfers through thethermal conductor and into the material to be sealed via the contactsurface.

Another aspect of the invention pertains to heat-seal device,comprising:

a. a heat source;

b. a thermal conductor, which encapsulates at least a portion of theheat source and is capable of transferring heat from the heat source viaa heat-seal contact surface on the thermal conductor, wherein thecontact surface is adapted to be brought into contact with a material tobe sealed; and

c. a temperature-measuring device, at least a portion of which isencapsulated with the heat source in the thermal conductor.

A further aspect of the invention pertains to a heat-seal system,comprising:

a. a heat-seal device, comprising

-   -   1) a heat source capable of producing heat,    -   2) a thermal conductor, which encapsulates at least a portion of        the heat source and is capable of assuming a temperature that        corresponds, at least in part, to the heat produced by the heat        source, and    -   3) a thermal insulator, which substantially surrounds the        thermal conductor but leaves a portion thereof exposed, the        exposed portion of the thermal conductor providing a heat-seal        contact surface, which is adapted to be brought into contact        with a material to be sealed;

b. a temperature-measuring device, at least a portion of which isencapsulated with the heat source in the thermal conductor; and

c. a controller in operative communication with the heat source and withthe temperature-measuring device, the controller adapted to

-   -   1) receive input from the temperature-measuring device, which is        indicative of the temperature of the thermal conductor, and    -   2) send output to the heat source, which causes the heat source        to produce more heat, less heat, or an unchanged amount of heat,

whereby, the controller determines the temperature of the thermalconductor.

These and other aspects and features of the invention may be betterunderstood with reference to the following description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of heat-seal system 10 in accordance with thepresent invention, including a heat-seal device 12 and controller 16;

FIG. 2 is a perspective view of the heat-seal device 12 illustrated inFIG. 1, showing the top of the device;

FIG. 3 is a perspective view of the heat-seal device 12 illustrated inFIG. 1, showing the bottom of the device;

FIG. 4 is a perspective view of a heat-source 24, which is a componentof heat-seal device 12;

FIG. 5 is a perspective view of a step in the assembly process forheat-seal device 12, in which the heat-source 24 is inserted into thehousing 18 of the device;

FIG. 6 is a perspective view of a step in the assembly process forheat-seal device 12, in which temperature-measuring device 48 isinserted into the housing 18 of the device;

FIG. 7 is a partial, perspective view of the device as shown in FIG. 6,following the insertion of the temperature-measuring device 48;

FIG. 8 is cross-sectional view of the device 12, taken along lines 8-8in FIG. 2; and

FIG. 9 is a schematic view of a heat-seal process employing system 10 asshown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one embodiment of a heat-seal system 10 in accordancewith the present invention. As illustrated, heat-seal system 10 mayinclude a heat-seal device 12, a support member 14, and a controller 16.Heat-seal system 10 may be employed in any of the above-described typesof machines for making packaging cushions, e.g., either air-filledcushions or foam-filled cushions, by securing the support member 14 tothe machine in such a manner as to bring the heat-seal device 12 intosliding contact with the film plies to be sealed together, i.e., to forma longitudinal seal as described above.

In this embodiment, heat-seal device 12 is in the form of a replaceablecartridge, which is removably affixed to support member 14. Theadvantage of this embodiment is ease of maintenance and replacement ofthe heat-seal device 12 when necessary, without having to remove theentire support member 14 from the machine in which the heat-seal system10 is employed. The components of the heat-seal device may thus becontained within a cartridge housing 18, with grip members 20 a, bincluded on either side of the cartridge housing to facilitate manualgrasping thereof. As shown, the grip members 20 a, b may be shaped tofit within corresponding slots 22 a, b in support member 14.

Referring collectively to FIGS. 1-4, it may be seen that heat-sealdevice 12 may comprise a heat source 24, a thermal conductor 26, and athermal insulator 28. As shown in FIG. 4, heat source 24 may comprise aheating element 30 and a pair of contact posts 32 a, b, wherein theheating element 30 is in physical and electrical contact with thecontact posts 32 a, b. Contact posts 32 a, b may extend through and outof housing 18 in such a manner as to provide electrical contact withsupply and return wires 34 a, b, respectively. As shown in FIG. 1,support member 14 may be configured such that supply wire 34 a extendsthrough the support member, and terminates at contact well 36 a, intowhich contact post 32 a may be inserted to make electrical contact withwire 34 a. Similarly, return wire 34 b may also extend through thesupport member 14, and terminate at contact well 36 b, into whichcontact post 32 b may be inserted to make electrical contact with wire34 b. In this manner, when wires 34 a, b are connected to a source ofelectricity, e.g., via controller 16, electricity may be supplied to theheat source 24 when heat-seal device 12 is inserted into support member14. As explained in further detail below, system 10 may be arranged suchthat controller 16 controls the amount of electricity supplied to heatsource 24, and thereby controls the amount of heat generated by the heatsource.

Heating element 30 may be any device capable of heating to a temperaturesufficient to heat-seal, i.e., melt bond or weld, two film pliestogether. Such temperature, i.e., the “sealing temperature,” may readilybe determined by those of ordinary skill in the art, without undueexperimentation, for a given application based on, e.g., the compositionand thickness of the film plies to be sealed together, the pressure atwhich the film plies and the heating device are urged together, thespeed at which the film plies are conveyed, etc., as noted above.

Suitable types of devices for heating element 30 include one or morewires, ribbons, bands, etc., comprising metal and/or other electricallyconductive materials. FIG. 4 illustrates heating element 30 in the formof a wire. When heating element 30 assumes such a form, the wire mayhave any desired cross-sectional shape, including round, square, oval,rectangular, etc.

In a preferred embodiment of the invention, heating element 30 has ahigher degree of electrical resistance than the contact posts 32 a, b.In this manner, the transmission of electrical current through the heatsource 24 results in the heating element 30 heating to a highertemperature than the contact posts 32 a, b due to the higher resistanceof the heating element. Thus, depending upon the difference inresistance between the heating element 30 and contact posts 32 a, b,only the heating element 30, and not the contact posts 32 a, b, may beheated to the sealing temperature. Such arrangement is advantageous inthat it results in less overall heat generated by the heat source 24,and therefore less energy usage. Further, when only the heating elementportion 30 of the heat source 24 is heated to the sealing temperature,the relatively small thermal mass of the heating element 30 may beheated to the sealing temperature from room temperature very quickly,usually in less than 1 second. Thus, the heat source 24 does not have tobe kept warm during pauses in sealing operations by maintaining a low or“idling” current through the heat source. Instead, current is sentthrough the heat source 24 just prior to initiation of a sealingoperation, and is then stopped immediately thereafter.

The difference in electrical resistance between the heating element 30and the contact posts 32 a, b may be accomplished by constructingheating element 30 from a material having a higher degree of electricalresistance and/or a smaller cross-section than that from which thecontact posts 32 a, b are constructed. Suitable materials from whichheating element 30 may be constructed include nickel/chromium alloy(nichrome), cobalt/chromium/nickel alloy, copper/manganese alloy,nickel/iron alloy, copper/nickel alloy, and other metals having arelatively high degree of electrical resistance. Contact posts 32 a, bmay be constructed from lower-resistance materials, such as stainlesssteel, brass, copper and copper alloys, materials such as steal with anexternal cladding of copper, gold, or highly conductive metal, and othermetals having a relatively low degree of electrical resistance.

Heating element 30 may be in the form of a wire having a diameterranging from about 0.003 inch to about 0.040 inch, e.g., between about0.005 to about 0.015 inch. Contact posts 32 a, b may have diameterranging from about 0.015 inch to about 0.125 inch, e.g., between about0.030 to about 0.060 inch.

The heat source 24 as illustrated in FIG. 4 may be constructed byproviding grooves 38 at a first end 40 of each of the contact posts 32a, b, placing the heating element 30 in such grooves, and affixing theheating element 30 to contact posts 32 a, b within the grooves 38, e.g.,via laser welding, electron beam welding, etc. As an alternative togrooves 38, holes may be drilled into the contact posts 32 a, b nearfirst end 40, into which opposing ends of the heating element 30 may beplaced. The second ends 42 of the contact posts 32 a, b may be shaped asnecessary to facilitate the making of good electrical contact withincontact wells 36 a, b in support member 14.

As perhaps best shown in FIGS. 2 and 8, thermal insulator 28substantially surrounds the thermal conductor 26, but leaves a portion44 thereof, i.e., a surface portion, exposed, wherein the exposedportion 44 provides a heat-seal contact surface. In some embodiments,the entire cartridge housing 18 may function as the thermal insulator,e.g., by being constructed from a thermally insulating material. Inother embodiments, the thermal insulator 28 may be omitted altogether.In still other embodiments, cartridge housing 18 may be constructedlargely from a relatively low-cost, non-insulating material, e.g.,plastic, metal, etc., with a thermally-insulating sub-housing or linerin direct contact with all or most of the thermal conductor 26.

In the drawings, the latter embodiment is illustrated, wherein thermalinsulator 28 is in the form of a liner or sub-housing within cartridgehousing 18. As shown, thermal insulator 28 is configured such that it issubstantially positioned between the thermal conductor 26 and thecartridge housing 18, thereby insulating the housing 18 from theconductor 26, particularly those portions of the conductor 26 that areadjacent to the heating element 30. In this manner, most of the heatgenerated by the heat source 24 will be transferred through the thermalconductor 26 and out of the conductor at surface portion 44, rather thaninto the cartridge housing 18. This improves the efficiency of theheat-sealing process and allows cartridge housing 18 to be constructed,e.g., from a low-cost plastic material having a melting point lower thanthe sealing temperature reached by the heat source 24.

With continuing reference to FIGS. 2 and 8, it may be seen that thermalconductor 26 encapsulates at least a portion of heat source 24. Forexample, as shown, the heating element 30 of heat source 24 may besubstantially completely encapsulated by the thermal conductor 26. Inthis manner, the heating element 30 may be physically protected by theconductor 26, which extends the service life of the element, e.g., bypreventing the heating element from coming into direct contact with thefilms to be sealed. Encapsulation in this manner also minimizes theexposure of the heating element to air, which thereby prevents orreduces oxidation of the heating element and further extends the servicelife thereof.

The thermal conductor 26 is capable of transferring heat from the heatsource 24. Thus, in addition to encapsulating the heating element 30,the thermal conductor 26 also functions as a heat transfer medium todeliver heat from the heat source 24 to the film being sealed. In thismanner, the conductor 26 further protects the heating element 30 byserving as a heat sink, which helps to prevent the heating element fromoverheating.

Accordingly, the thermal conductor 26 preferably has a relatively highdegree of thermal conductivity while the thermal insulator 28 has arelatively low degree of thermal conductivity. Thermal conductivity is ameasure of the ability of a material to transmit heat, and is defined asthe rate at which heat will flow through the material. The lower thethermal conductivity of a material is, the better the material is atresisting the flow of heat therethrough. Conversely, the higher theconductivity, the better the material is at allowing heat to flowthrough it. One common unit of measurement is Btu in./ft.² hour ° F.,which is the rate of heat flow, in BTU's per hour, through a square footof material one inch thick whose surfaces have a temperaturedifferential of 1° F. For reference, water has a conductivity of 4 Btuin./ft.² hour ° F., fiberglass insulation is approximately 0.04, andstainless steel is 111.

The specific thermal conductivity of the materials chosen for thethermal conductor 26 and thermal insulator 28 is not critical; however,it is preferred that the thermal conductivity of the material chosen forthe conductor 26 is higher than that of the material selected for theinsulator 28 such that the thermal conductor 26 has a higher degree ofthermal conductivity than the thermal insulator 28.

Preferably, the thermal conductor 26 will have a relatively high degreeof thermal conductivity in order to transfer heat as efficiently aspossible, e.g., greater than about 1 Btu in./ft.² hour ° F. In addition,the material employed for the thermal conductor 26 preferably also has asufficiently low degree of electrical conductivity that the electricalcurrent sent through the supply/return wires 34 a, b will pass throughthe heating element 30, and not through the thermal conductor 26. Thematerial used for the thermal conductor 26 will ideally also have asufficiently high operating temperature to withstand the heat producedby the heat source 24. A further factor in the selection of materialsfor thermal conductor 26 is abrasion resistance. As described in furtherdetail below, when the heat-seal device 12 is in operation, the surface44 of the conductor 26 is in sliding contact with the film being sealed,and sufficient abrasion resistance to provide a reasonable life span isthus a desirable feature.

A number of suitable compounds for thermal conductor 26 are available,including high-temperature epoxies and ceramic cements. Many epoxieshave a maximum temperature rating of around 500° F., while ceramiccements have maximum temperature ratings ranging from about 1500° to4000° F. A specific material that was found to work well as a thermalconductor is an alumina ceramic cement sold by Cotronics Corporation ofBrooklyn, N.Y. under the tradename Resbond 989FS. This alumina ceramiccement has a temperature rating of 3000° F., a thermal conductivity of15 Btu in./ft.² hour ° F., good abrasion properties, and a relativelylow degree of electrical conductivity. Other suitable materials includezircon-based cements, and aluminum-nitride-filled ceramic pottingcompounds.

The thermal insulator 28 preferably has a relatively low degree ofthermal conductivity, i.e., in comparison to the thermal conductor 26,in order to insulate the cartridge housing 18 from the heat generated bythe heat source 24, and to direct such heat into the film being sealed.For example, the thermal conductivity of the material from which thethermal insulator 28 is constructed is preferably less than about 5 Btuin./ft.² hour ° F. Many suitable materials exist, e.g., ceramics, suchas zirconia and alumina silicate, high temperature plastics such as polyether ether keytone (PEEK) or polyphenylsulfone, glass, glass ceramics,etc. A specific example of a suitable thermal insulating material is ageneral purpose alumina silicate ceramic, such as Grade GCGW-5110,manufactured by Graphtek, LLC, which has a thermal conductivity of 0.003Btu in./ft.² hour ° F.

As noted above, the thermal insulator 28 substantially surrounds thethermal conductor 26, but leaves a surface portion 44 thereof exposed.In this manner, the exposed surface portion 44 provides a heat-sealcontact surface, which is adapted to be brought into contact with amaterial to be sealed, e.g., a pair of juxtaposed film plies. Theexposed portion 44 may be adapted in this regard, e.g, by applyingthereto a surface finish, which both smoothes and rounds the exposedportion so that it may be brought into sliding contact with filmmaterial to be sealed with minimal abrasion thereto and/or frictionalresistance therewith. If desired, the entire contact surface 46 of theheat-seal device 12 may be rounded and smoothed in this manner.

The heat source 24 is preferably encapsulated by thermal conductor 26such that substantially no portion of the heat-source, and particularlythe heating element 30 thereof, is exposed at the exposed/heat-sealcontact surface 44. In this manner, the heat source 24 does not comeinto direct contact with the material to be sealed. Instead, the heatgenerated by the heat source 24 is transferred into the thermalconductor 26. By substantially surrounding the thermal conductor 26 withthe thermal insulator 28 as described above, a significant portion ofthe heat transferred into the thermal conductor 26 by the heat source 24may be transferred through the thermal conductor 26 and into a materialto be sealed via the exposed/heat-seal contact surface 44.

As may be appreciated, the foregoing configuration in accordance withthe present invention results in a highly efficient transfer of theenergy supplied to heat source 24, e.g., electrical energy via wires 34a, b, into the film or other material to be sealed. In addition, thisconfiguration avoids the above-noted difficulties associated withconventional heat-sealing devices, which generally employ direct contactbetween the film and the heat-source. That is, by encapsulating theheat-source, the problems of ‘ribbon cutting’ of the film and shortenedservice life of the heating element are avoided.

In accordance with another aspect of the present invention, heat-sealdevice 12 may further include a temperature-measuring device 48, atleast a portion of which is encapsulated with heat source 24 in thermalconductor 26, as shown in FIG. 8. In the illustrated embodiment, athermocouple is used as the temperature-measuring device 48, whichincludes two wires 50, 52 of dissimilar metals welded together at ajunction 54. As is well known to those of ordinary skill in the art,thermocouples operate based on the principle that when a junction of twodissimilar metals is heated, a voltage is created that corresponds tothe temperature. Typically, the junction size is 1.5 times the wirediameter. For instance, if the wires 50, 52 are both 0.005 inches indiameter, the junction 54 will be 0.0075 inches in diameter.

There are numerous, commercially-available thermocouple types usingvarious materials which are chosen for their temperature ranges andresponse time. Almost any type will work in heat-seal device 12, e.g., a‘type J’ thermocouple comprising, as the two dissimilar metals, iron andconstantan, with a temperature range of 32-1382° F. In most cases, thetemperature needed to seal two polymeric film plies together is in therange of 250-400° F. The output of a type J thermocouple in thistemperature range is approximately 6 to 8 millivolts. Since this outputis small, the controller 16 will preferably include an instrumentamplifier that will increase and filter the signal from thethermocouple.

As shown in FIG. 8, both the heating element 30 of heat source 24 andthe thermocouple junction 54 of temperature-measuring device 48 may beencapsulated in the thermal conductor 26, which is surrounded by thethermal insulator 28 in the cartridge housing 18. As shown, the heatingelement 30 and thermocouple junction 54 may be physically separated fromeach other within the thermal conductor 26. When the thermal conductor26 is formed from a material having a relatively low degree ofelectrical conductivity, this arrangement results in the heating element30 and thermocouple junction 54 being electrically insulated from oneanother, which makes for a clearer output signal from the thermocouple.

The encapsulated portion of the temperature-measuring device 48 may bepositioned between the heat source 24 and heat-seal contact surface 44.For example, as also shown in FIG. 8, the thermocouple junction 54 canbe placed between the heating element 30 and the heat-seal contactsurface 44. This configuration has been found to result in a high degreeof accuracy in the measurement of the temperature of the thermalconductor 26 at the surface 44. The encapsulation of the junction 54 andheating element 30 in the thermal conductor 26 ensures that suchconfiguration will be maintained, e.g., will not be disturbed due tomovement of the film against the heat-seal device 12. Alternatively, theencapsulated portion of the temperature-measuring device 48, e.g., thejunction 54 thereof when device 48 is a thermocouple, may be positionedbeneath or beside the heat source 24 within the thermal conductor 26.

Referring now to FIGS. 5-7, a method for assembling the heat-seal device12 will be described. FIG. 5 shows the beginning of the assemblyprocess, with thermal insulator 28 having already been inserted intocartridge housing 18. As shown, the thermal insulator 28 has an openchannel 56 to accommodate the heat source 24.

The thermal conductor 26 may be provided in the form of an uncuredliquid or paste, which may subsequently be cured into a solid. Forexample, alumina ceramic cement, e.g., Resbond 989FS, has the ability toflow when in uncured/liquid form, and then accept a smooth finish whenin cured/solid form. Curing may be accomplished by simply allowing thematerial to air dry.

Accordingly, a small quantity of uncured thermal conducting material mayfirst be poured or otherwise placed into the channel 56, e.g., in anamount sufficient to cover the bottom 58 of the channel 56 (FIG. 8). Theheat source 24 is then inserted in the direction of arrows 60 intochannel 56 (FIG. 5), and pressed down into the channel until the secondends 42 of the contact posts 32 a, b protrude from the bottom 62 of thehousing 18 (FIG. 3) and the heating element 30 is buried into thethermal conducting material placed at the bottom 58 of the channel 56.

In FIG. 6, the heat source 24 has been fully installed, with only thesecond ends 42 of the contact posts 32 a, b visible, as extending fromthe bottom 62 of the housing 18. Additional thermal conducting material,indicated at 64, is then added into the channel 56, on top of theheating element 30 to bury the element 30.

FIG. 6 also depicts the installation of the temperature-measuring device48. In the presently-illustrated embodiment, thermal insulator 28 mayinclude a second channel 66 to accommodate the temperature-measuringdevice 48. Second channel 66 may be disposed at an angle relative to thechannel 56, e.g., substantially transverse as shown. Both channels 56and 66 may extend beyond thermal insulator 28 as needed, e.g., intohousing 18 as shown.

The temperature-measuring device 48 may be inserted into the secondchannel 66 as shown, i.e., by moving the device 48 into the channel 66in the direction of arrow 68, such that it is embedded into the thermalconducting material 64. As a result, the temperature-measuring device 48and heat source 24 will have the respective positions shown in FIG. 7(the thermal conducting material 64 is not shown in FIG. 7 for clarity).

After installation of the temperature-measuring device 48, additionalthermal conducting material 64 is added on top of the device 48, so thatthe material 64 covers the device 48 and fills the channels 56, 66. Ifdesired, the thermal conducting material 64 may be mounded above the topof the channels 56, 66 to insure complete fill. The conducting material64 may then be allowed to cure completely until hardened (with the rateand conditions of the cure depending upon the specific materialselected), thereby resulting in the thermal conducting material 64transforming into thermal conductor 26. Any excess material may beremoved by sanding, and the heat-seal contact surface 44 may bealternatively or additionally polished to provide a desired degree ofsmoothness, e.g., to minimize the coefficient of friction between thesurface 44 and the films to be sealed.

The result of the foregoing assembly process is the heat-seal device 12as shown in FIG. 2.

Referring back to FIG. 1, it may be seen that the temperature-measuringdevice 48 may be brought into electrical communication with controller16 in the same manner as is heat source 24, i.e., via support member 14.Support member 14 may thus be configured such that sensing wire 70 aextends through the support member, and terminates at contact pin 72 a,while sensing wire 70 b extends through the support member, andterminates at contact pin 72 b as shown. Within heat-seal device 12,thermocouple wire 50 terminates at, and is electrically connected to,thermocouple contact 74, which, as shown in FIG. 3, is positioned at thebottom 62 of housing 18, e.g., as a step in the assembly process forheat-seal device 12. Similarly, thermocouple wire 52 terminates at, andis electrically connected to, thermocouple contact 76. In thisembodiment, the thermocouple contacts 74, 76 are included to ensure goodelectrical communication between the relatively small-diameterthermocouple wires 50, 52 and the sensing wires 70 a, b, by electricallyconnecting the thermocouple wires 50, 52 to the relatively large contactsurfaces 78, 80, against which the contact pins 72 a, b abut when theheat-seal device 12 is inserted into support member 14 as shown in FIG.1.

Referring now to FIG. 9, a heat-sealing method in accordance with thepresent invention will be described. FIG. 9 illustrates system 10, asshown in FIG. 1, in a process for sealing a web of material, e.g., forsealing together two juxtaposed film plies 82 a, b via a continuouslongitudinal seal, e.g., at juxtaposed edges of the film plies tothereby form an inflatable or Tillable packaging material 85 with aclosed longitudinal edge (closed edge not shown). As is conventional,film plies 82 a, b may be supplied from separate film rolls 84 a, b.Sealing may be facilitated by providing a backing member 86, which maybe movable relative to heat-seal device 12, or simply biased against theheat-seal device, such that film plies 82 a, b may be compressed betweendevice 12 and member 86 during sealing as shown.

The system may further include a conveyance mechanism for conveying aweb of material to be sealed, e.g., juxtaposed film plies 82 a, b,against the heat-seal contact surface 44 of heat-seal device 12, whereinthe conveyance mechanism is adapted to convey the web at varying speeds.As shown, the conveyance mechanism may be embodied by a pair of driven,counter-rotating nip rollers 88 a, b. As an alternative, the conveyancemechanism may be embodied by a single drive roller, which is used inplace of backing member 86 to both drive the conveyance of the web andcompress the web against the heat-seal device 12.

In its most basic form, the method illustrated in FIG. 9 includes thesteps of:

a. providing heat-seal device 12;

b. causing the heat source 24 to produce heat; and

c. bringing the heat-seal contact surface 44 into contact with thematerial to be sealed, i.e., film ply 82 a, which is juxtaposed withfilm ply 82 b as shown. In this manner, as explained above, the heatproduced by heat source 24 transfers through the thermal conductor 26and into the film plies 82 a, b via contact surface 44 of heat-sealdevice 12.

When the heat-seal device 12 includes temperature-measuring device 48,the foregoing method would include the further step of measuring thetemperature within the thermal conductor 26. Such method may be carriedout by system 10, as shown in FIGS. 1 and 9, wherein controller 16 is inoperative communication with both heat source 24 and withtemperature-measuring device 48, i.e., via respective wires 34 a, b and70 a, b as described above. Controller 16 may thus be adapted, e.g.,programmed, to:

1) receive input from temperature-measuring device 48, which isindicative of the temperature of thermal conductor 26, and

2) send output to heat source 24, which causes the heat source toproduce more heat, less heat, or an unchanged amount of heat, e.g.,depending upon a selected/target temperature that is provided to, orcalculated by, controller 16.

In this manner, controller 16 determines the temperature of the thermalconductor, which will generally vary within a temperature range that iscentered on a selected temperature, which becomes a target temperaturethat the controller tries to maintain. Controller 16 may thus include anoperator interface 90 (FIG. 9), e.g., a control panel, which allows anoperator to select a temperature for the thermal conductor 26.Alternatively, controller 16 may be programmed with a mathematicalalgorithm that calculates the selected/target temperature, based onvarious factors such as film speed, film type, etc.

As may be appreciated, the controller 16, temperature-measuring device48, and heat source 24 together form a temperature-control feedbackloop, in which the controller will continuously vary the power inputsupplied to the heat source, based on temperature feedback provided bythe temperature-measuring device, in order to maintain the temperatureof the thermal conductor 26 as closely as possible to theoperator-selected or controller-calculated temperature. As with all suchtemperature-control feedback loops, there will generally be an inherentoff-set between the selected temperature and the actual temperature,with the controller 16 continually ‘driving’ the actual, sensedtemperature toward the set-point temperature, in response to changes inthe actual temperature due to operational changes during the sealingprocess. Controller 16 will thus maintain the thermal conductor 26 at atemperature that falls within a range of the selected temperature.

Many types of controllers are suitable for use as controller 16.Controller 16 may be an electronic controller, such as a printed circuitassembly containing a micro controller unit (MCU), which storespre-programmed operating codes; a programmable logic controller (PLC); apersonal computer (PC); or other such control device which allows thetemperature of the thermal conductor 26 to be controlled via localcontrol, e.g., via operator interface 90; remote control; pre-programmedcontrol, etc.

Various modes of control may be employed by controller 16, includingproportional, derivative, integral, and combinations thereof, e.g., PID(proportional-integral-derivative) control, to achieve a desired degreeof accuracy in the control of the temperature of thermal conductor 26,e.g., a desired maximum degree of off-set between the set and actualtemperature. The electrical power output to heat source 24 fromcontroller 16 may be regulated via analog power control or digital powercontrol, e.g., pulse width modulated power control.

In some embodiments, the film web to be sealed is conveyed, i.e.,driven, through the system at variable speeds. See, e.g., thefoam-in-place system disclosed in U.S. Pat. No. 7,607,911, thedisclosure of which is hereby incorporated entirely herein by referencethereto. In such systems, as the film drive speed is increased, the timeof contact between the sealing surface and the film becomes shorter. Asthe contact time decreases in this manner, the temperature of thesealing surface may be raised in order to ensure that good sealscontinue to be made, i.e., in order to put sufficient heat into the filmto ensure that its temperature remains above the melting point thereof.Conversely, when the film speed is decreased, the contact time betweenthe sealing surface and the film increases. In this case, thetemperature of the sealing surface may be lowered to ensure that thesealing surface does not put so much heat into the film that it meltstherethrough. Accordingly, controller 16 may be adapted, e.g.,programmed, to change the temperature of the thermal conductor 26 basedon changes in the speed at which the film web is conveyed.

As an example, the heat-seal device 12 was used as a longitudinalsealing device in the foam-in-place apparatus disclosed in theabove-referenced U.S. Pat. No. 7,607,911, by mounting the device 12 onshaft 48 of the '911 apparatus such that the heat-seal contact surface44 of the device 12 was urged into contact with drive roller 40 of the'911 apparatus near an end of the drive roller such that the unsealedlongitudinal edges of a pair of juxtaposed film plies were sealedtogether when conveyed between the contact surface 44 of the device 12and drive roller 40 of the '911 apparatus. The film plies comprisedpolyethylene and had a thickness of about 0.75 mil.

The drive roller 40 of the '911 apparatus was driven by a gear motorthat included an encoder. A controller, similar to controller 16 asdescribed above, was in communication with the encoder and gear motor,such that the controller monitored the film drive speed (based on inputfrom the encoder) and drove it at a desired rate in accordance with the'911 patent. The encoder produced 3900 counts per inch of film travel.Thus, for example, if the controller read 3900 counts per second, thismeant that the film was being driven at 1 inch per second.

The controller may be programmed to simply increase the seal temperatureby a predetermined amount in response to a given speed increase, e.g., atemperature increase of 10° F. for each 1 inch/second speed increase,and visa versa. Alternatively, optimal ‘seal-temperature vs. film-speed’values may be determined experimentally, and then programmed into thecontroller. The latter was accomplished by driving the film pliesthrough the '911 apparatus at various speeds throughout the speed rangeof the gear motor, and determining the lowest and highest temperaturesat each speed at which a good seal was made. A “good seal” at the lowesttemperature was the point at which the film plies exhibited some degreeof stretch prior to the seal breaking when the film plies were pulledapart, indicating that the seal was strong enough to withstand at leastsome amount of applied tensile force. A “good seal” at the hightemperature was the point just below the temperature when ribbon cuttingbegan.

Table 1 below is a summary of the resultant data:

TABLE 1 Film drive Low temp High temp Temp Calculated speed for good forgood midpoint temp: (inch/min.) seal (° F.) seal (° F.) (° F.) Y = mX +b 1 200 230 215 218 2 220 260 240 236 3 220 280 250 253 4 230 310 270270 5 240 350 295 288 6 240 360 300 305 7 260 390 325 323 8 260 410 335340 9 290 430 360 357 10 300 450 375 375

The film plies were driven from 1 to 10 inches/minute in increments of 1inch/minute. The temperature values shown in Table 1 were obtainedexperimentally at each speed. To determine the low temperature for agood seal, the seal temperature was lowered until the seal failed. Thetemperature was then raised until ribbon cutting occurred to determinethe high temperature for a good seal. The values shown in Table 1 arethe average results of numerous seal tests. The temperature midpoint isthe value midway between the low and high values. This midpoint valuemay be used by the controller to determine the target temperature foreach speed value since it offers the largest range to account forinconsistencies in the operation of the apparatus.

There are several ways that the foregoing data can be used by thecontroller to determine the target temperature for the heat-seal device12. In one embodiment, the data from Table 1 or the like may beprogrammed into the controller, which uses the data to select the propertemperature value, e.g., the temperature midpoint, based on theselected/detected film drive speed. For instance, if the film drivespeed is 5 inches/minute, the corresponding midpoint heat-sealtemperature is 295° F.

In an alternative embodiment, a liner regression formula may be used todetermine the target temperature, given that the values in Table 1represent a substantially straight line. Thus, the formula

Y=mX+b

may be used by the controller, where “Y” is the target temperature, “m”is the slope, “X” is the drive speed, and “b” is the Y intercept. In asituation where the speed vs. temperature plot is not linear, a higherorder equation can be used. For the data set forth in Table 1, the slopeis 1.742 and the intercept is 200.67. These values may be used by thecontroller to calculate target temperature as a result of film drivespeed. The film drive speed may be determined by the controller based onfeedback from the gear motor encoder. The last column in Table 1 aboveshows the target temperature as calculated in this manner.

Accordingly, the controller may monitor and/or control the film drivespeed, and continuously calculate and update the target temperaturebased on the drive speed. Thus, as the drive speed changes, so does thetemperature of the seal element. When the controller both monitors andcontrols the drive speed it can, as an alternative, use its target drivespeed rather than measured drive speed for temperature calculations.

The controller may also be programmed to anticipate changes in drivespeed and, therefore, temperature, for those embodiments in which thecontroller determines drive speed, given that the controller will thus“know” when a speed change will occur, and what the next drive speed andtarget temperature will be. Such anticipation can be used during a cyclewhenever the drive speed changes. If, for instance, the drive speedincreases from 2 inches/minute to 8 inches/minute, the controller cantake the heating element 30 to the requisite target temperature, e.g.,increase the temperature from 236° F. to 340° F., at a time prior tochanging speeds, which may help to maintain the consistency andintegrity of the seal, e.g., by not allowing unsealed gaps to formimmediately following the speed increase. Conversely, the controller canlower the target temperature prior to slowing or stopping the filmdrive. This may prevent the heat-seal device 12 from burning through thefilm due to having too much heat for the slower speed.

The foregoing description of preferred embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention.

1. A heat-seal device, comprising: a. a heat source; b. a thermalconductor, which encapsulates at least a portion of said heat source andis capable of transferring heat from said heat source; and c. a thermalinsulator, which substantially surrounds said thermal conductor butleaves a portion thereof exposed, said exposed portion of said thermalconductor providing a heat-seal contact surface, which is adapted to bebrought into contact with a material to be sealed, wherein, said thermalconductor has a higher degree of thermal conductivity than said thermalinsulator.
 2. The heat-seal device of claim 1, wherein said heat sourceis encapsulated by said thermal conductor such that substantially noportion of said heat-source is exposed at said heat-seal contactsurface, whereby, said heat source does not come into direct contactwith the material to be sealed.
 3. The heat-seal device of claim 1,further including a temperature-measuring device, at least a portion ofwhich is encapsulated with said heat source in said thermal conductor.4. A heat-sealing method, comprising the steps of: a. providing theheat-seal device of claim 1; b. causing said heat source to produceheat; and c. bringing said heat-seal contact surface into contact with amaterial to be sealed, whereby, the heat produced by said heat sourcetransfers through said thermal conductor and into the material to besealed via said contact surface.
 5. A heat-sealing method, comprisingthe steps of: a. providing the heat-seal device of claim 3; b. causingsaid heat source to produce heat, thereby effecting a change intemperature within said thermal conductor; c. measuring the temperaturewithin said thermal conductor; d. bringing said heat-seal contactsurface into contact with a material to be sealed, whereby, the heatproduced by said heat source transfers through said thermal conductorand into the material to be sealed via said contact surface.
 6. Theheat-seal device of claim 3, wherein the encapsulated portion of saidtemperature-measuring device is positioned between said heat source andsaid heat-seal contact surface.
 7. A heat-seal device, comprising: a. aheat source; b. a thermal conductor, which encapsulates at least aportion of said heat source and is capable of transferring heat fromsaid heat source via a heat-seal contact surface on said thermalconductor, wherein said contact surface is adapted to be brought intocontact with a material to be sealed; and c. a temperature-measuringdevice, at least a portion of which is encapsulated with said heatsource in said thermal conductor.
 8. A heat-seal system, comprising: a.a heat-seal device, comprising 1) a heat source capable of producingheat, 2) a thermal conductor, which encapsulates at least a portion ofsaid heat source and is capable of assuming a temperature thatcorresponds, at least in part, to the heat produced by said heat source,and 3) a thermal insulator, which substantially surrounds said thermalconductor but leaves a portion thereof exposed, said exposed portion ofsaid thermal conductor providing a heat-seal contact surface, which isadapted to be brought into contact with a material to be sealed; b. atemperature-measuring device, at least a portion of which isencapsulated with said heat source in said thermal conductor; and c. acontroller in operative communication with said heat source and withsaid temperature-measuring device, said controller adapted to 1) receiveinput from said temperature-measuring device, which is indicative of thetemperature of said thermal conductor, and 2) send output to said heatsource, which causes said heat source to produce more heat, less heat,or an unchanged amount of heat, whereby, said controller determines thetemperature of said thermal conductor.
 9. The system of claim 8, whereinsaid controller maintains said thermal conductor at a temperature thatfalls within a range of a selected temperature.
 10. The system of claim8, wherein a. said system further includes a conveyance mechanism forconveying a web of material to be sealed against said heat-seal contactsurface of said heat-seal device, said conveyance mechanism beingadapted to convey the web at varying speeds; and b. said controller isadapted to change the temperature of said thermal conductor based onchanges in the speed at which the web is conveyed.